ES2957033A2 - Preparation method for isophosphorite iron-type iron phosphate and application thereof - Google Patents

Abstract

The present disclosure relates to the field of battery material recovery. Disclosed are a preparation method for isophosphorite iron-type iron phosphate and an application thereof. The method comprises the following steps: mixing lithium iron phosphate with a solvent and adding an acidic solution to adjust the pH to be acidic, so as to obtain an acidic lithium iron phosphate solution; adding a transition metal additive into the acidic lithium iron phosphate solution; and performing microenvironment strengthening, a leaching reaction, and filtering to obtain isophosphorite iron-type iron phosphate and a lithium-rich solution. According to the present invention, lithium iron phosphate and water are mixed and an acid is added to maintain the pH between 2 and 6, and then a nickel-cobalt-manganese transition metal additive is added by means of a microenvironment strengthening method to realize a surface catalyzation and strengthening reaction, so as to promote the generation of hydroxyl radicals and greatly improve a rate of oxidization of divalent iron, thereby implementing selective leaching of lithium under an oxygen/air condition, wherein the leaching rate of lithium in a leaching solution reaches 90.5-99.9%, and the contents of iron and phosphorus in the leaching solution are both lower than 0.1 ppm.

Description

DESCRIPTION

PREPARATION METHOD OF HETEROSITE TYPE IRON PHOSPHATE

AND APPLICATION OF THE SAME

TECHNICAL FIELD

The invention relates to the technical field of battery recycling and, in particular, to a method of preparing heterosite-type iron phosphate and the application thereof.

BACKGROUND

In recent years, with the rapid increase in the production of electronic and electrical equipment, the demand for lithium-ion batteries has also continued to increase. However, lithium-ion batteries have a limited lifespan, so a large amount of lithium-ion battery waste is produced every year. If these lithium-ion batteries cannot be recycled properly, serious environmental and resource problems will arise. On the one hand, lithium-ion batteries contain high levels of valuable metals, such as lithium, nickel, cobalt and manganese, the content of which in lithium-ion batteries is much higher than their average mineral content. If metals cannot be recycled properly, a huge waste of resources will occur; On the other hand, heavy metals and harmful electrolytes in lithium-ion battery waste will also cause potential harm to the natural environment and human health. If these lithium-ion batteries can be effectively recycled, not only can a large amount of valuable metals be recovered and resource waste reduced, but also the pressure on ecological and environmental protection can be reduced.

Among cathode materials for lithium-ion batteries, ternary cathode materials and LiFePO4 cathode materials occupy considerable market share due to their excellent performance. Among ternary cathode materials, lithium, nickel, cobalt and manganese are valuable metals with high recovery value, while in LiFePO4 cathode materials, lithium has high recovery value. Therefore, LiFePO4 cathode recovery is mainly focused on lithium recovery. At present, the recovery of lithium iron phosphate cathode materials is mainly carried out through wet technology, which comprises the following modes: (1) Excess acid or excess oxidant completely leaches lithium iron phosphate to obtain a mixture, and then adjust the pH of the mixture to precipitate FePO42H2O by binding Fe3+ and PO4<3->, and then a lithium-containing solution is obtained; (2) The stoichiometric ratio of acid and oxidant selectively leaches lithium to obtain a solution containing lithium and iron phosphate. The iron phosphate recovered by these two methods is mainly precipitated in the form of FePO42H2O, which is difficult to dissolve in acid. To further recover iron and phosphorus resources, calcination is needed before FePO42H2O can be dissolved, making recovery of iron and phosphorus resources difficult. At the same time, the oxidants used in the leaching process of the above methods are mainly chemical reagents such as hydrogen peroxide, persulfate, sodium hypochlorite, etc., and the leaching cost is high.

Therefore, there is an urgent need to develop a lithium iron phosphate recovery process with high leaching selectivity, low leaching cost and short recovery process.

SUMMARY OF THE INVENTION

An objective of the present invention is to provide a method of preparation and application of heterosite type iron phosphate, addressing the problems of the prior art regarding the recovery of iron phosphate such as poor selectivity for lithium extraction, high consumption of agents, long recovery process and low product value. By providing an improved process, the direct preparation of lithium phosphate from heterosite is achieved while obtaining the advantages of low impurity content in the leaching solution, high lithium concentration, low agent consumption and high lithium recovery rate .

To achieve the aforementioned objective, the following technical solution is adopted in the invention.

A method of preparing heterosite type iron phosphate comprises the following steps:

(1) Mix lithium iron phosphate with a solvent to obtain a suspension, add acid solution, and adjust the suspension to acidic pH to obtain acidic lithium iron phosphate liquid;

(2) Add a transition metal additive to the acidic lithium iron phosphate liquid to obtain a mixture, carry out leaching of the mixture in an intensifying microenvironment, followed by filtration to obtain a heterosite type iron phosphate and a rich solution in lithium; leaching in an intensifying microenvironment consists of extracting iron phosphate from the acidic lithium iron phosphate liquid with microbubbles or under controlled pressure;

Heterosite type iron phosphate is a product obtained by delithiation of an olivine type lithium iron phosphate. Currently, there are many crystalline phases of iron phosphate reported in the literature: orthorhombic heterosite-type iron phosphate formed by delithiation of lithium iron phosphate, monoclinic iron phosphate, orthorhombic iron phosphate or iron phosphate of crystals of quartz a; Its aqueous phase comprises monoclinic iron phosphate dihydrate and orthorhombic iron phosphate dihydrate.

Preferably, in step (1), the lithium iron phosphate is recovered from the residual lithium iron phosphate cathode materials.

More preferably, lithium iron phosphate is obtained by discharging, pulverizing and screening residual lithium iron phosphate cathode materials; Lithium iron phosphate mainly contains the elements Li, P, Fe, Al, C and O.

Preferably, in step (1), the solvent is water.

Preferably, in step (1), the acid solution used to adjust the pH is at least one selected from the group consisting of sulfuric acid, nitric acid and hydrochloric acid.

More preferably, the acid solution has a concentration of 0.5-5 mol/l.

The acid solution above is to provide hydrogen ions and maintain the pH during the leaching process.

Preferably, in step (1), adjusting the suspension to an acidic pH is to adjust the pH of the suspension to 2-6.

Preferably, the microbubbles are produced by introducing a gas into the lithium iron phosphate acid liquid, and the gas is air or oxygen. One method of oxygen enhancement is to increase the oxidizing capacity and mass transfer efficiency of oxygen by intensifying the microenvironment, that is, using the self-pressurization effect of microbubbles or oxygen-enriched pressure-raising media to improve the effect of oxidation of oxygen, and achieve the object of leaching iron phosphate in a weak acid condition.

More preferably, the microbubbles produced by introducing a gas into the lithium iron phosphate acid liquid have a diameter of 10-50 ^m.

More preferably, the controlled pressure is 0.05-1 MPa.

Preferably, in step (2), the transition metal additive is at least one selected from the group consisting of nickel oxide, cobalt tetroxide, manganese dioxide, lithium cobaltate, lithium nickelate, lithium manganate or manganate lithium nickel cobalt.

Preferably, in step (2), the lithium iron phosphate acid liquid and the transition metal additive are in a volume and mass ratio of 50-400 g/L.

Preferably, in step (2), the transition metal additive is added in an amount of 0.5-6% of the amount of lithium iron phosphate.

Nickel cobalt manganese transition metal additive is introduced to catalyze the surface oxygen microbubbles/microbubbles produced by pressure control/dissolved oxygen to generate strongly oxidizing hydroxyl radicals, to improve the oxidizing capacity of divalent iron and its oxidation rate. oxidation reaction.

Preferably, in step (2), leaching is carried out at a temperature of 25 °C-80 °C for 30-240 min.

There are three main methods for leaching lithium iron phosphate. Method (I) involves oxidative leaching of lithium iron phosphate under strong acidic conditions to obtain a solution containing Li+, Fe3+ and PO4<3->, and then adjusting the pH of the solution to obtain a precipitated iron phosphate by the union of Fe3+ and PO4<3->; Method (II) involves leaching lithium iron phosphate in moderate acidity to obtain a solution containing Li+, Fe2+ and PO4<3->, and then using a strong oxidant to oxidize Fe2+ in the leaching solution to Fe3+, and then binding of Fe3+ with PO4<3->to form iron phosphate precipitation to achieve selective leaching. Method (III) is a selective leaching of lithium iron phosphate through direct oxidation and delithiation of lithium iron phosphate using strong oxidizing agents under weak acid conditions and produces isomanganese iron phosphate. In this method, due to the low mass transfer and oxidation potential of oxygen, although the oxidation of Fe2+ can be achieved to a certain extent, the oxidation capacity is weak. Therefore, in the actual process, intensifiers such as hydrogen peroxide, sodium persulfate, sodium hypochlorite and ozone are often used as oxidants to achieve Fe2+ oxidation. When oxygen/air is used as an oxidant to leach the lithium iron phosphate cathode material, the oxidation of Fe2+ cannot be carried out effectively, resulting in high Fe2+ content in the leaching solution and poor selective leaching of lithium. Therefore, it is necessary to improve the oxygen oxidation capacity to achieve efficient and selective leaching of lithium.

It can be seen from formula (1) that the oxidation potential of oxygen/air is related to the pH and pressure of the solution, that is, increasing the oxygen pressure and reducing the pH of the solution can increase the oxidation potential. oxidation of oxygen and increase the oxidizing capacity of oxygen. But lowering the pH of the solution will certainly lead to increased acid consumption and leaching of iron and phosphorus. Therefore, under weak acid conditions, the use of microenvironment intensification means to change the oxidation potential of oxygen in the solution can achieve selective leaching of lithium iron phosphate. Microbubbles have a self-pressurization effect, which can increase the oxygen oxidation potential by generating pressure changes in local microdomains. At the same time, active oxygen can also be generated on the surface of the microbubbles to greatly increase the oxidizing capacity of oxygen. The pressure control method can also increase the oxygen oxidation potential by changing the partial pressure of oxygen in the leaching environment. Therefore, by intensifying the microenvironment, the oxygen oxidation performance is improved.

On the other hand, when nickel-cobalt-manganese transition metal additives are present, microbubbles of oxygen or dissolved oxygen that increase the oxidizing capacity through pressurization of dissolved oxygen will generate strong oxidizing hydroxyl radicals under the surface catalysis of the transition metal additives, further improving the oxidizing capacity of oxygen/air and the oxidation capacity and oxidation reaction rate of ferrous iron. In this way, solid-phase oxidation of Fe2+ can be performed without additional addition of an oxidant, and direct solid-phase delithiation of lithium iron phosphate can be achieved to produce a heterosite-type iron phosphate product.

Preferably, in step (2), further purification of the lithium-rich solution comprises adjusting the pH of the lithium-rich solution, removing impurities from the solution, adding sodium carbonate to the solution, filtering and drying to obtain carbonate. lithium.

The present invention also provides the application of the above-mentioned preparation method in the preparation of battery cathode materials.

beneficial effects

The method of the present invention comprises mixing lithium iron phosphate with water to prepare a suspension and adding acid to the suspension to maintain the pH of the leachate between 2 and 6 during the process, and then adding a nickel transition metal additive manganese cobalt, combined at the same time with a microenvironment intensification medium to realize the catalytic surface enhancement reaction that promotes the generation of hydroxyl radicals and greatly increases the rate of oxidation reaction in divalent iron, to achieve Selective leaching of lithium under oxygen/air conditions. The leaching rate of lithium in the leaching solution reaches 90.5-99.9%, and both the iron and phosphorus contents in the leaching solution are less than 0.1 ppm; The recovered heterosite type iron phosphate has a purity of 99.9%, and the recovery rate of heterosite type iron phosphate is 99.3%.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flow chart of the process of Example 1 for recovering heterosite-type iron phosphate;

FIG. 2 is a schematic diagram of the leaching route of lithium iron phosphate;

FIG. 3 is an XRD pattern of the heterosite type iron phosphate recovered in Example 1.

DETAILED DESCRIPTION OF THE ILLUSTRATED EXAMPLES

To fully understand the present invention, the preferred experimental scheme of the present invention will now be described along with examples to further illustrate the features and advantages of the present invention. Any change or alteration that does not deviate from the essence of the present invention can be understood by those skilled in the art. The scope of protection of the invention is determined by the scope of the claims.

When specific conditions are not indicated in the examples of the present invention, this will be carried out under the conventional conditions or conditions recommended by the manufacturer. Raw materials, reagents, etc. used without indicating their manufacturers are all conventional commercially available products.

Example 1

A method of preparing the heterosite type iron phosphate of this embodiment comprises the following steps:

(1) Mix lithium iron phosphate and water in a mass-volume ratio of 50 g/L to obtain a suspension, and then add 2 mol/L of hydrochloric acid to the suspension to maintain the pH at 2 during the process of leaching to obtain an acidic lithium iron phosphate liquid;

(2) Add cobalt tetroxide to the acidic lithium iron phosphate liquid to obtain a mixture, and introduce oxygen into the mixture to generate microbubbles with a diameter of 50 μm to carry out leaching at 25 °C for 240 minutes; Once leaching is complete, filter the mixture to obtain a solution rich in lithium and heterosite-type iron phosphate. The leaching rate of lithium in the leaching solution reached 99.5%, and the iron content and phosphorus content in the leaching solution were less than 0.1 ppm.

Example 2

A method of preparing the heterosite type iron phosphate of this embodiment comprises the following steps:

(1) Mix lithium iron phosphate and water in a mass-volume ratio of 50 g/L to obtain a suspension, and then add 2 mol/L of hydrochloric acid to the suspension to maintain the pH at 6 during the process of leaching to obtain an acidic lithium iron phosphate liquid;

(2) Add manganese dioxide to the acidic lithium iron phosphate liquid to obtain a mixture, and introduce oxygen into the mixture to generate microbubbles with a diameter of 50 μm to carry out leaching at 25 °C for 240 minutes; Once leaching is complete, filter the mixture to obtain a solution rich in lithium and heterosite-type iron phosphate. The leaching rate of lithium in the leaching solution reached 93.9%, and the iron content and phosphorus content in the leaching solution were less than 0.01 ppm.

Example 3

A method of preparing the heterosite type iron phosphate of this embodiment comprises the following steps:

(1) Mix lithium iron phosphate and water in a mass-volume ratio of 400 g/L to obtain a suspension, and then add 2 mol/L hydrochloric acid to the suspension to maintain the pH at 2 during the process of leaching to obtain an acidic lithium iron phosphate liquid;

(2) Add lithium-nickel-cobalt manganate to the acidic lithium iron phosphate liquid to obtain a mixture, and introduce oxygen into the mixture to generate microbubbles with a diameter of 50 μm to carry out leaching at 25 °C for 240 minutes ; Once leaching is complete, filter the mixture to obtain a solution rich in lithium and heterosite-type iron phosphate. The leaching rate of lithium in the leaching solution reached 96.7%, and the iron content and phosphorus content in the leaching solution were less than 0.1 ppm.

Example 4

A method of preparing the isomorphic iron phosphate of this embodiment comprises the following steps:

(1) Mix lithium iron phosphate and water in a mass-volume ratio of 50 g/L to obtain a suspension, and then add 2 mol/L of hydrochloric acid to the suspension to maintain the pH at 6 during the process of leaching to obtain an acidic lithium iron phosphate liquid;

(2) Add manganese dioxide to the acidic lithium iron phosphate liquid to obtain a mixture, and introduce oxygen into the mixture to generate microbubbles with a diameter of 10 μm to perform leaching at 25 °C for 240 min. Once leaching is complete, filter the mixture to obtain a solution rich in lithium and heterosite-type iron phosphate. The leaching rate of lithium in the leaching solution reached 98.6%, and the iron content and phosphorus content in the leaching solution were less than 0.01 ppm.

Example 5

A method of preparing the heterosite type iron phosphate of this embodiment comprises the following steps:

(1) Mix lithium iron phosphate and water in a mass-volume ratio of 50 g/L to obtain a suspension, and then add 2 mol/L of hydrochloric acid to the suspension to maintain the pH at 6 during the process of leaching to obtain an acidic lithium iron phosphate liquid;

(2) Add manganese dioxide to the acidic lithium iron phosphate liquid to obtain a mixture, and introduce oxygen into the mixture to generate microbubbles with a diameter of 10 μm to perform leaching at 80 °C for 240 min. Once leaching is complete, filter the mixture to obtain a solution rich in lithium and heterosite-type iron phosphate. The leaching rate of lithium in the leaching solution reached 99.5%, and the iron content and phosphorus content in the leaching solution were less than 0.01 ppm.

Example 6

A method of preparing the heterosite type iron phosphate of this embodiment comprises the following steps:

(1) Mix lithium iron phosphate and water in a mass-volume ratio of 50 g/L to obtain a suspension, and then add 2 mol/L of hydrochloric acid to the suspension to maintain the pH at 6 during the process of leaching to obtain an acidic lithium iron phosphate liquid;

(2) Add lithium manganate to the acidic lithium iron phosphate liquid to obtain a mixture, and introduce oxygen into the mixture to generate microbubbles with a diameter of 10 μm to perform leaching at 25 °C for 240 min. Once leaching is complete, filter the mixture to obtain a solution rich in lithium and heterosite-type iron phosphate. The leaching rate of lithium in the leaching solution reached 90.5%, and the iron content and phosphorus content in the leaching solution were less than 0.01 ppm.

Experiment 7

A method of preparing the heterosite type iron phosphate of this embodiment comprises the following steps:

(1) Mix lithium iron phosphate and water at a mass-volume ratio of 400 g/L to obtain a suspension, and then add 2 mol/L hydrochloric acid to the suspension to maintain the pH at 6 during the process of leaching to obtain an acidic lithium iron phosphate liquid;

(2) Add manganese dioxide to the lithium iron phosphate acid liquid to obtain a mixture, and introduce oxygen into the mixture to generate microbubbles with a diameter of 10 μm and perform leaching at an oxygen pressure of 0.05 MPa, leaching was carried out at 80 °C for 240 min. Once leaching is complete, filter the mixture to obtain a solution rich in lithium and heterosite-type iron phosphate. The leaching rate of lithium in the leaching solution reached 90.5%, and the iron content and phosphorus content in the leaching solution were less than 0.01 ppm.

Experiment 8

A method of preparing the heterosite type iron phosphate of this embodiment comprises the following steps:

(1) Mix lithium iron phosphate and water in a mass-volume ratio of 50 g/L to obtain a suspension, and then add 2 mol/L of hydrochloric acid to the suspension to maintain the pH at 6 during the process of leaching to obtain an acidic lithium iron phosphate liquid;

(2) Add lithium manganate to the acidic lithium iron phosphate liquid to obtain a mixture, and introduce oxygen into the mixture at a pressure of 1 MPa, to carry out leaching at 80 °C for 240 min. Once leaching is complete, filter the mixture to obtain a solution rich in lithium and heterosite-type iron phosphate. The leaching rate of lithium in the leaching solution reached 99.9%, and the iron content and phosphorus content in the leaching solution were less than 0.01 ppm.

Experiment 9

A method of preparing the heterosite type iron phosphate of this embodiment comprises the following steps:

(1) Mix lithium iron phosphate and water in a mass-volume ratio of 400 g/L to obtain a suspension, and then add 2 mol/L hydrochloric acid to the suspension to maintain the pH at 2 during the process of leaching to obtain an acidic lithium iron phosphate liquid;

(2) Add lithium nickelate to the acidic lithium iron phosphate liquid to obtain a mixture, and introduce oxygen into the mixture to generate microbubbles with a diameter of 50 μm, to carry out leaching at 25 °C for 240 min. Once leaching is complete, filter the mixture to obtain a solution rich in lithium and heterosite-type iron phosphate. The leaching rate of lithium in the leaching solution reached 99.9%, and the iron content and phosphorus content in the leaching solution were less than 0.1 ppm.

Experiment 10

A method of preparing the heterosite type iron phosphate of this embodiment comprises the following steps:

(1) Mix lithium iron phosphate and water in a mass-volume ratio of 400 g/L to obtain a suspension, and then add 2 mol/L hydrochloric acid to the suspension to maintain the pH at 2 during the process of leaching to obtain an acidic lithium iron phosphate liquid;

(2) Add nickel oxide to the acidic lithium iron phosphate liquid to obtain a mixture, and introduce oxygen into the mixture to generate microbubbles with a diameter of 50 μm, to carry out leaching at 80 °C for 30 min. Once leaching is complete, filter the mixture to obtain a solution rich in lithium and heterosite-type iron phosphate. The leaching rate of lithium in the leaching solution reached 91.5%, and the iron content and phosphorus content in the leaching solution were less than 0.1 ppm.

Comparative example

A method of preparing the heterosite type iron phosphate of this embodiment comprises the following steps:

Mix lithium iron phosphate and water at a mass-volume ratio of 400 g/L to obtain a suspension, and then add an acid to the suspension to maintain the pH at 2 during the leaching process to obtain an acidic lithium iron phosphate liquid. iron and lithium; introduce oxygen into the mixture at normal pressure to carry out leaching at 80 °C for 30 min. Once leaching is complete, filter the mixture to obtain a solution rich in lithium and heterosite-type iron phosphate. The leaching rate of lithium in the leaching solution was 58.13%, and the leaching rates of iron and phosphorus in the leaching solution were 10.67% and 9.75%, respectively.

Comparison of results

1.Recovery rate

T l 1 T r r i n l Ex rim n 1 E m l m r iv

.Purity

Table 2 Element content in the lithium-rich solution

Table 3 Purity of the recovered ti iron phosphate or heterosite

Performance test:

Lithium iron phosphate prepared from the iron phosphate recovered in Examples 1-3 above and the Comparative Example were used as the cathode, with graphite being used as the anode. A battery was assembled with the cathode and anode and its first discharge test was carried out at a rate of 1C.

Tab 4 Performance test results

The results are shown in Table 4. At a rate of 0.1C, the first discharge capacity of the lithium iron phosphate cathode material recovered in the present invention is greater than that of the heterosite type iron phosphate recovered in the traditional method, and the first discharge capacity of Example 1 is 157.1 mAh/g, while the specific capacity of the comparative example is only 155.6 mAh/g.

Figure 1 shows the flow chart of the heterosite type iron phosphate recovery process of Example 1. From Figure 1, it can be concluded that by subjecting the lithium iron phosphate to pulping, adjusting the pH value, leaching With intensification of the microenvironment and performing solid-liquid separation, a heterosite-type iron phosphate can be obtained.

In FIG. 2 illustrates that there are three main methods for leaching lithium iron phosphate. Method (I) involves oxidative leaching of lithium iron phosphate under strong acidic conditions to obtain a solution containing Li+, Fe3+ and PO4<3->, and then adjusting the pH of the solution to obtain a precipitated iron phosphate by the union of Fe3+ and PO4<3->; Method (II) involves leaching lithium iron phosphate in moderate acidity to obtain a solution containing Li+, Fe2+ and PO4<3->, and then using a strong oxidant to oxidize Fe2+ in the leaching solution to Fe3+, and then binding of Fe3+ with PO4<3->to form iron phosphate precipitation to achieve selective leaching. Method (III) is a selective leaching of lithium iron phosphate through direct oxidation and delithiation of lithium iron phosphate using strong oxidizing agents under weak acid conditions and produces a heterosite type iron phosphate. In this method, due to the low mass transfer and oxidation potential of oxygen, although the oxidation of Fe2+ can be achieved to a certain extent, the oxidation capacity is weak. Therefore, in the actual process, intensifiers such as hydrogen peroxide, sodium persulfate, sodium hypochlorite and ozone are often used as oxidants to achieve Fe2+ oxidation. When oxygen/air is used as an oxidant to leach the lithium iron phosphate cathode material, the oxidation of Fe2+ cannot be carried out effectively, resulting in high Fe2+ content in the leaching solution and poor selective leaching of lithium. Therefore, it is necessary to improve the oxygen oxidation capacity to achieve efficient and selective leaching of lithium.

It can be seen from the the reaction, and LiFePO4 participates in the reaction to generate FePO4 in a new phase. The Li in the cathode material reacts to form soluble lithium salt, which enters the solution.

The preparation method and application of a heterosite type iron phosphate provided by the present invention have been described in detail above. Specific examples are used in this article to illustrate the principle and implementation of the present invention. The description of the above examples is only used to help understand the method and central idea of the present invention, including the best way, and also allows any person skilled in the art to practice the present invention, including making and using any device or system, and implement any combined method. It should be noted that, for those of ordinary skill in the art, without departing from the principle of the present invention, various improvements and modifications can be made to the present invention, and these improvements and modifications are also included within the scope of protection of the claims of the present invention. The scope of patent protection of the present invention is defined by the claims and may include other embodiments that those skilled in the art may think of. If these other embodiments have structural elements that do not differ from the literal expression of the claims, or if they include equivalent structural elements that do not differ substantially from the literal expression of the claims, these other embodiments must also be included in the scope of the claims.

Claims (10)

1. A method of preparing heterosite type iron phosphate, comprising the following steps: (1) Mix lithium iron phosphate with a solvent to obtain a suspension, adjust the suspension to acidic pH to obtain acidic lithium iron phosphate liquid; (2) Add a transition metal additive to the acidic lithium iron phosphate liquid to obtain a mixture, perform leaching of the mixture in an intensifying microenvironment, followed by filtration to obtain the heterosite type iron phosphate and a rich solution in lithium; Leaching in the intensifying microenvironment consists of extracting iron phosphate from the acidic lithium iron phosphate liquid with microbubbles or under controlled pressure. 2. The preparation method according to claim 1, wherein in step (1), adjusting the suspension to the acidic pH is carried out by adding a liquid acid to the suspension, wherein the liquid acid is at least one selected from the group consisting of sulfuric acid, nitric acid and hydrochloric acid; and the liquid acid has a concentration of 0.5-5 mol/l. 3. The preparation method according to claim 1, wherein in step (1), adjusting the suspension to the acidic pH is adjusting to a pH of 2-6. 4. The preparation method according to claim 1, wherein in step (1), the lithium iron phosphate is recovered from a residual lithium iron phosphate cathode material. 5. The preparation method according to claim 1, wherein the microbubbles are generated by introducing a gas into the lithium iron phosphate acid liquid, wherein the gas is air or oxygen; The microbubbles generated by introducing the gas into the acidic lithium iron phosphate liquid have diameters of 10-50 |jm. 6. The preparation method according to claim 1, wherein the controlled pressure is 0.05-1 MPa. 7. The preparation method according to claim 1, wherein in step (2), the transition metal additive is at least one selected from the group consisting of nickel oxide, cobalt tetroxide, manganese dioxide, lithium cobaltate, lithium nickelate, lithium manganate and lithium-nickel-cobalt manganate. 8. The preparation method according to claim 1, wherein in step (2), the lithium iron phosphate acid liquid and the transition metal additive are in a mass-volume ratio of 50-400 g /l. 9. The preparation method according to claim 1, wherein in step (2), the lithium-rich solution is subjected to a purification process comprising the following steps: adjusting the lithium-rich solution to an alkaline pH ; remove impurities to obtain a purified solution; then add sodium carbonate to the purified solution to react; filter and dry a resulting precipitate to obtain lithium carbonate. 10. Application of the preparation method of any one of claims 1-9 in the preparation of a battery cathode material.